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<title>Debugging with GDB: Type Checking</title>

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<a name="An-Overview-of-Type-Checking"></a>
<h4 class="subsection">15.3.1 An Overview of Type Checking</h4>

<p>Some languages, such as C and C<tt>++</tt>, are strongly typed, meaning that the
arguments to operators and functions have to be of the correct type,
otherwise an error occurs.  These checks prevent type mismatch
errors from ever causing any run-time problems.  For example,
</p>
<div class="smallexample">
<pre class="smallexample">int klass::my_method(char *b) { return  b ? 1 : 2; }

(gdb) print obj.my_method (0)
$1 = 2
</pre><pre class="smallexample">but
</pre><pre class="smallexample">(gdb) print obj.my_method (0x1234)
Cannot resolve method klass::my_method to any overloaded instance
</pre></div>

<p>The second example fails because in C<tt>++</tt> the integer constant
&lsquo;<samp>0x1234</samp>&rsquo; is not type-compatible with the pointer parameter type.
</p>
<p>For the expressions you use in <small>GDB</small> commands, you can tell
<small>GDB</small> to not enforce strict type checking or
to treat any mismatches as errors and abandon the expression;
When type checking is disabled, <small>GDB</small> successfully evaluates
expressions like the second example above.
</p>
<p>Even if type checking is off, there may be other reasons
related to type that prevent <small>GDB</small> from evaluating an expression.
For instance, <small>GDB</small> does not know how to add an <code>int</code> and
a <code>struct foo</code>.  These particular type errors have nothing to do
with the language in use and usually arise from expressions which make
little sense to evaluate anyway.
</p>
<p><small>GDB</small> provides some additional commands for controlling type checking:
</p>
<a name="index-set-check-type"></a>
<a name="index-show-check-type"></a>
<dl compact="compact">
<dt><code>set check type on</code></dt>
<dt><code>set check type off</code></dt>
<dd><p>Set strict type checking on or off.  If any type mismatches occur in
evaluating an expression while type checking is on, <small>GDB</small> prints a
message and aborts evaluation of the expression.
</p>
</dd>
<dt><code>show check type</code></dt>
<dd><p>Show the current setting of type checking and whether <small>GDB</small>
is enforcing strict type checking rules.
</p></dd>
</dl>

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